1. Field of the Invention
The present disclosure is related to armor. More particularly, the present disclosure is related to multilayer armor made of materials such as glass, glass-ceramic, or plastics, with improved multi-hit capabilities.
2. Description of Related Art
Ballistic rounds tend to have a high aspect ratio, where the length of the round is several times longer than the diameter of the round, and where the round itself is constructed of hardened steel or tungsten carbide or the like.
It is well known to those accomplished in the art of designing, developing, manufacturing, testing ballistic armor that the armor makes a stronger and more secure defeat of the incoming round if that round is caused to “turn” once it impacts and starts to penetrate the armor.
The key reason a turning projectile is considered so favorable to defeating the incoming projectile is that as soon as the projectile is turned it is facing a far thicker cross section of armor as the angle created by the turning significantly increases the distance to the back face. Stated another way, the aspect ratio of the projectile is not just very large, where the area of the pointed tip has a dramatically smaller surface area than the surface area of the side of the projectile. Thus, turning the projectile refers to changing its angle of incidence with respect to the armor so that more of the larger aspect ratio sides impact the target than the smaller aspect ratio tip.
Turning is also thought to significantly reduce the velocity and energy of the projectile since the area of the projectile interacting with the armor translates from the cross section described by the z axis to one described by it length and part of its diameter.
Additionally, the turning of incoming projectiles also changes the profile of energy and kinetic transfer from the tip of the projectile to the armor to the cross section described by the surface area of the side of the projectile to the armor. In addition, it imparts torque loads that can bend or break the round.
In many cases the prior art armor, especially in the case of opaque armor, has focused on construction and geometries designed to cause the turning of the incoming round. In other prior art armor, ceramic shapes such as pyramids, balls and the like have been assembled into the strike face or body of such armor to assure the turning of the round such as the structures seen in U.S. Pat. Nos. 7,603,939, 7,736,474, 7,077,048, and 7,562,612.
In still other prior art armor, granular media has been used to influence the turning of projectiles, where the turning is effected by the features of the granules such as size, density, packing, depth, etc. and their ability to impose lateral displacement and angular momentum such as the structures seen in U.S. Pat. No. 7,827,897, International Publication No. WO0192810, the article by S. K. Dwividi et al., “Two dimensional mesoscale simulations of projectile penetration into dry sand,” J. Appl. Phys. 104 (2008), and the article by Todd P. Broyles, “An Evaluation of the PENCURV Model for Penetration Events in Complex Targets,” Sandia report, SAND2004-3482.
Still further, prior art armor has used the inclusion of gaps or spaces within the armor to encourage turning of projectiles as seen in U.S. Publication No. 20090217813 and U.S. Pat. No. 7,908,973.
Unfortunately, many of these prior art techniques for turning the projectile cannot be applied to transparent armor as the transparency will be diminished or eliminated by the structures describe by much of this prior art.
Therefore, it has been determined by the present disclosure that armor, particularly transparent glass-ceramic armor, that enhances the turning of incoming round, particularly second rounds, is a valuable way to make more reliable and robust armor, and also a way to make the armor less weighty.